Fig. 1:

Abscisic Acid-mediated regulation of plasmodesmata and symplastic transport. High Abscisic Acid (ABA) levels regulate the expression of plasmodesmata (PD) proteins involved in callose synthesis/ degradation (such as callose synthases: CALS, PD located protein like kinase: PDLP and β-1, 3 glucanases: BG) among other PD regulators. Callose accumulation at PD leads to the formation of sphincters that restrict symplastic transport. Research from Kitagawa et�al. (2019) and others indicates that changes in PD width, number and frequency of secondary PD (independent of callose levels) also contribute to ABA-mediated responses. How, mechanistically, these changes are orchestrated is not yet known. The outcome, however, is a restriction in the symplastic transport of specific mobile proteins including those that function as growth promoter factors during bud dormancy, or on the cell-to-cell spreading of viruses and other pathogens and/or other environmental responses. Discontinuous arrows show hypothetical relations.